Additional West Nile virus (WNV) cases have been diagnosed by the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL). The number of WNV positive cases in Texas now totals ten.
As of August 24, 2015, TVMDL can confirm horses in the following counties tested positive for WNV.
- Houston County
- Atascosa County
- Jefferson County
- Roberts County
- Sterling County
- Parker County
- Randall County
- Liberty County
- Scurry County
- Hutchinson County
As with earlier reported positive cases, the affected horses were not previously vaccinated against the disease.
WNV is a viral disease that normally cycles between wild birds and mosquitoes. As the virus infection rate increases in birds it is more likely to be spread to mosquitos that in turn bite horses and humans. The virus abruptly attacks the central nervous system. In the U.S., clinical signs for WNV develop in only 10-39 percent of infected horses. The death rate among U.S. horses ranges from 30 to 40 percent for West Nile disease. Of horses that recover from the disease, up to 40 percent may exhibit neurological signs for six months or more after the initial diagnosis.
Though the TVMDL Serology Section has received numerous requests for Eastern Equine Encephalitis testing, the number of positive cases remains at 7 for 2015.
EEE is a viral disease that also normally cycles between wild birds and mosquitoes. As the virus infection rate increases in birds it is more likely to be transmitted by an infected mosquito that bites horses and humans. The virus abruptly attacks the central nervous system. As with WNV, EEE cannot be transmitted from horse to horse, or from a horse to a human. Horses and humans are considered “dead-end” hosts, meaning if infected they cannot transmit the virus back to feeding mosquitoes.
Symptoms for other neurologic diseases can present similarly; diagnostic testing is the only method to definitively determine infection. In order to have a complete diagnostic picture, TVMDL also recommends veterinarians request additional tests including: Equine Herpesvirus-1, Western Equine Encephalitis and Venezuelan Equine Encephalitis.
As a zoonotic disease of interest, when a WNV case is confirmed positive TVMDL notifies the Texas Animal Health Commission (TAHC). Human infection with WNV is known to occur in the U.S. However, horse to human transmission is not a concern. TVMDL, TAHC and the Texas Department of State Health Services have information related to West Nile virus and mosquito control available for free download. For more information on TVMDL’s equine neurologic testing, visit tvmdl.tamu.edu, or contact the agency headquarters at 1.888.646.5623.